The present invention relates to baluns and, more specifically, to a compact, broadband, flexible printed circuit balun utilizing a six-port network.
Baluns are used to provide an impedance-matched transition between a balanced and an unbalanced transmission line. They have been implemented in a variety of ways, such as with lumped constant reactive components.
At higher frequencies (e.g., microwave), the performance of a balun becomes critical from the point of view of both size and performance. For example, in a microwave antenna array, each antenna element may require an individual balun near the antenna element itself. This dictates a design that is compact and, due to the potentially large numbers needed in a large antenna array, low cost.
A typical prior art balun consists of a coaxial twin lead cable and a 180xc2x0 hybrid transformer. This balun is both bulky and expensive. To overcome these difficulties, a slotline balun utilizing a metal (e.g., aluminum) substrate with the slotline etched in the aluminum was developed, as shown in FIG. 1. In this design, a transition region was used to couple a coaxial connector to the slotline, which was subsequently coupled to a slot radiator. While this design exhibited improved electrical performance over other baluns of the prior art, it was still expensive and did not provide the broadband performance required for certain antenna-related applications. Because it was a rigid metal structure, it exhibited excessive stress concentration points that made it inherently unreliable. In addition, the manufacturing cost was objectionably high.
It is therefore an object of the invention to provide a compact slotline balun having a wide operating bandwidth.
It is a further object of the invention to provide a compact slotline balun having a wide operating bandwidth utilizing a six-port network.
It is an additional object of the invention to provide a compact slotline balun having a low insertion loss across a wide operating bandwidth.
It is another object of the invention to provide a compact slotline balun having a thin cross section for implementation on a printed circuit card.
It is a still further object of the invention to provide a compact slotline balun having a very low manufacturing cost.
It is yet another object of the invention to provide a compact slotline balun having good dimensional stability to ensure high performance reliability.
It is a still further object of the invention to provide a compact slotline balun which may be readily integrated with patch antenna elements formed using conventional printed circuit technology.
It is an additional object of the invention to provide a compact printed circuit slotline balun which is flexible.
In accordance with the present invention, there is provided a compact slotline balun implemented on a 10-mil thick printed circuit card. The inventive balun utilizes a transition region configuration of a six-port network to achieve a good impedance match and low insertion loss across a wide operating band. The balun is typically manufactured using standard printed circuit techniques which yield a thin, flexible, dimensionally stable device.